1. Field of the Invention
The present invention relates to a sheet finisher that executes a finishing processing, such as hole punching, etc., to a sheet ejected from an image forming apparatus.
2. Prior Art
There have been disclosed various types of a sheet finisher that receives sheets ejected from the image forming apparatus and punches binding holes (punching holes) at specific positions, and is used in installation close to the image forming apparatus.
Such a sheet finisher includes two types: one that temporarily collects sheets conveyed into a tray and then punches binding holes on the sheets collectively, and another one that punches binding holes on the sheet one by one on the way of conveyance.
The former holds an inconvenience that the collective punching will not permit such a processing as collation, sorting, paper jogging, etc., after punching. On the other hand, the latter holds an inconvenience being unsuitable for a high-speed punching, because the punching on the way of the conveyance of the sheet temporarily stops the conveyance thereof, and accordingly the subsequent sheet cannot be conveyed during the punching.
In an attempt to dissolve such inconveniences, a finisher by the rotary puncher has been proposed which can execute to a sheet the finishing, such as collation, sorting, paper jogging, etc., and which can punch the sheet without stopping the conveyance (refer to Japanese Laid Open Patent Publication No. Hei 6-135620).
In the finisher that temporarily stops the conveyance of a sheet on the way thereof and punches the sheet, the leading edge of the sheet is blocked by the resist roller so as to temporarily halt the conveyance, and the sheet is punched. Since the trailing edge of the sheet is still under conveyance during the punching, the sheet makes a loop as a whole during this period; and when the conveyance of the sheet is restarted, the loop of the sheet is dissolved.
Therefore, the spacing S between the preceding sheet and the succeeding sheet to be punched needs more than the spacing that corresponds to the total time T of the time t1 required for punching the preceding sheet and the time t2 required for the loop of the preceding sheet dissolving (T=t1+t2). If the conveyance speed of the sheet is given by V, the spacing will be expressed by S=Vxc3x97T. That is, the preceding sheet and the succeeding sheet need to secure at least the foregoing spacing S between them.
Accordingly, to enhance the processing capacity needs to increase the conveyance speed, and to shorten the time required for the hole punching; however, the conveyance speed is subjected to the restriction by the speed of the sheet ejected from the image forming apparatus, which cannot be changed. Accordingly, to enhance the processing capacity needs to increase the punching speed, but to increase the speed involves size enlargement of the apparatus, creation of noises, and dispersion of hole positions, which are inconvenient.
And, in the finishing by the foregoing rotary puncher, it is not needed to give a spacing between the preceding sheet and the succeeding sheet, but since the leading edge of the sheet is not made to be blocked by the resist roller, the leading edge thereof becomes irregular, so that the hole positions become dispersed, which is also inconvenient.
A major object of the invention is to provide a novel sheet puncher that executes a punching to a sheet ejected from an image forming apparatus on the way of the conveyance while maintaining the conveyance speed of the ejected sheet.
Another object of the invention is to provide a novel image forming apparatus that executes a finishing processing such as a punching at a high speed on the way of the conveyance of the sheet while maintaining the conveyance speed of the sheet that has completed an image recording and is ejected from the image forming apparatus.
Another object of the invention is to provide a novel sheet finisher that executes a finishing processing such as a punching on the way of the conveyance to a sheet ejected from the image forming apparatus while maintaining the conveyance speed of the ejected sheet.
Another object of the invention is to provide a novel sheet puncher that temporarily increases the speed of one conveyance roller disposed upstream in the conveyance direction, of a pair of conveyance rollers disposed along the conveyance direction of the sheet, operates a punching mechanism when the trailing edge of the sheet to be conveyed is brought in a temporal halt, and executes a precise punching at a specific position on the sheet.
Other objects and features of the invention will become apparent from the detailed description of the invention in conjunction with the accompanying drawings.